1. Field of the Invention
The present invention relates to a seat belt retractor. More particularly, the present invention relates to an electrically actuatable locking mechanism which prevents seat belt webbing withdrawal from the retractor.
2. Description of the Prior Art
Seat belt retractors are known. One type of seat belt retractor is web-sensitive. A web-sensitive seat belt retractor has a locking mechanism which locks to prevent withdrawal of seat belt webbing in response to withdrawal of the belt webbing above a predetermined rate of acceleration which occurs in certain emergency situations. There are many known actuators for actuating the locking mechanism to prevent belt webbing withdrawal. Typically, the locking mechanism is actuated by relative rotation of the retractor spool on which the webbing is wound and an inertia member. In response to a predetermined amount of relative rotation therebetween, a pawl pivots into engagement with a ratchet wheel attached to the spool to prevent rotation of the spool and thus prevent further seat belt webbing withdrawal.
It is well known that to maximize occupant safety during an emergency situation, the seat belt webbing should be locked from withdrawal as quickly as possible after the start of the emergency situation in order to minimize the amount of occupant movement. This has resulted in the development of electrically actuated locking mechanisms.
German Published Application No. 2,402,748 discloses a web-sensitive retractor which includes an eddy current brake to slow rotation of an inertia member upon energization of an electrical coil disposed adjacent the inertia member. Slowing rotation of the inertia member results in relative rotation between the inertia member and a seat belt spool to effect actuation of a mechanical locking mechanism. Thus, the German Published application discloses an electrically actuatable seat belt retractor locking mechanism.
Several other retractors are known which have electrically actuatable locking mechanisms. One such retractor is disclosed in U.S. Pat. No. 3,825,205. In U.S. Pat. No. 3,825,205, an electric signal is generated by a sensor in response to an emergency situation, such as sudden vehicle deceleration. The electric signal is conducted to a solenoid which acts to move a pawl into engagement with a ratchet wheel connected to a spool. When the pawl engages the ratchet wheel, rotation of the spool is blocked and further withdrawal of the seat belt webbing from the spool is prevented. In German Published Application No. 2,215,892, friction brakes are brought into direct engagement with a seat belt spool upon electrical energization of a device for moving the brakes. The brakes stop the spool from rotating to prevent seat belt withdrawal therefrom.